Fractional-N frequency synthesizers are essential parts of any modern multi-band and multi-standard wireless transceiver systems. These synthesizers make use of digital delta-sigma noise shaping modulators to generate the fractional division ratios. Delta-sigma modulators, however, comprise a finite state machine that generates cyclic train of division ratios. These introduce fractional spurious tones. In general, dithering and/or seeding are used to alleviate the presence of delta-sigma fractional spurs. In high performance application, however, dither and seeding techniques are not useful since they significantly increase in-band noise and introduce large frequency errors.